title: Functional and psychological variables both affect daily physical activity in COPD: a structural equations model.
abstract: BACKGROUND
  Daily physical activity (DPA) level is reduced in patients with COPD. The aim of this study was to investigate the association of DPA with functional and psychological variables in these patients.
  
  
  METHODS
  155 COPD patients (102 males, median (IQR) age 62 years (54-69 years), predicted FEV1 60% (40-75%) were included. We assessed DPA (DigiWalker SW-200), functional capacity and psychological factors.
  
  
  RESULTS
  DPA level was significantly associated with all functional capacity variables and two psychological variables (Perceived Physical Ability Subscale, depression subscale of the Hospital Anxiety and Depression Scale). The six-minute walking distance and St. George Respiratory Questionnaire activity score explained 37% of the variance of DPA in a regression analysis. A structural equations model revealed that psychological variables indirectly explained DPA through functional capacity variables. DPA was stronger associated with functional capacity variables and weaker with psychological variables in patients with lower functional status than in patients with higher functional status.
  
  
  CONCLUSIONS
  Higher levels of DPA are associated with better functional capacity, but interestingly, DPA is also affected by psychological factors, though only indirectly, via functional capacity. The effect of specific treatment addressing psychological factors on DPA level and exercise tolerance needs further investigation.
  
  
  BACKGROUND
  ClinicalTrials.gov, NCT00614796.
authors.affiliation: University of Groningen, University Medical Center Groningen, Department of Pulmonary Diseases, P.O. Box 30001, Internal Mail Address AA11, 9700 RB Groningen, The Netherlands; University of Groningen, University Medical Center Groningen, Center for Rehabilitation, Groningen, P.O. Box 30002, Internal Mail Address CD24, 9750 RA Haren, The Netherlands; University of Groningen, University Medical Center Groningen, Groningen Research Institute for Asthma and COPD, P.O. Box 30001, Internal Mail Address FA40, 9700RB Groningen, The Netherlands. Electronic address: w.a.altenburg@cvr.umcg.nl.
authors.forename: Wytske A
authors.initials: WA
authors.lastname: Altenburg
authors.forename: Linda
authors.initials: L
authors.lastname: Bossenbroek
authors.forename: Mathieu H G
authors.initials: MH
authors.lastname: de Greef
authors.forename: Huib A M
authors.initials: HA
authors.lastname: Kerstjens
authors.forename: Nick H T
authors.initials: NH
authors.lastname: ten Hacken
authors.forename: Johan B
authors.initials: JB
authors.lastname: Wempe
mesh_terms: D000328:Adult; D000368:Aged; D001007:Anxiety / Q000209:etiology / Q000503:physiopathology / Q000523:psychology; D003376:Counseling; D003863:Depression / Q000209:etiology / Q000503:physiopathology / Q000523:psychology; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009042:Motivation; D009043:Motor Activity / Q000502:physiology*; D011594:Psychometrics; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000523:psychology* / Q000534:rehabilitation; D020377:Self Efficacy
keywords: 6MWD; CCQ; COPD; Clinical COPD Questionnaire; DEFS; DPA; Dutch Exertion and Fatigue Scale; FEV(1); Forced Expiration Volume in one second; Functional capacity; GARS; GOLD; Groningen Activity and Restriction Scale; HADS; Hospital Anxiety and Depression Scale; IQR; PPAS; PR; Perceived Physical Ability Subscale; Physical activity; Psychological capacity; RMSEA; RV%TLC; SEM; SF-36; SGRQ; SPSS; SRQ-E; Scientific Package of Social Sciences; Self-Regulation Questionnaire for Exercise; Short Form 36; St. George Respiratory Questionnaire; Structural equations model; VO(2)peak; chronic obstructive pulmonary disease; daily physical activity; global initiative for chronic obstructive lung disease; interquartile range; peak oxygen uptake; pulmonary rehabilitation; residual volume as percentage of total lung capacity; root mean square error of approximation; six-minute walking distance; structural equations modeling